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BIOL241 > W2 L4a - Evolving on Land: The Amniotes > Flashcards

W2 L4a - Evolving on Land: The Amniotes Flashcards

1
Q

What are the 4 phylogenetically distinct groups in the Amniotes?

A
  1. Synapsida (Mammals & Mammal-like reptiles)
  2. Testudines (Turtles)
  3. Archosauromprha (Crocodiles, Dinosaurs, & Birds)
  4. Lepidosauromorpha (Lizards and Snakes)
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2
Q

What is a clade?

A

A group consisting of a single common ancestor and all it’s descendants

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3
Q

What does the cladogram of extant tetrapods look like?

A

—————————————— Amphibians
Synapsids
Turtles A
Turtles B
Sphenodon
Lizards
Snakes
Crocodiles
Birds

  • Synapsids and under are Amniotes *
    ** Turtles and under are Sauropsids **
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4
Q

When did Amniotes evolve on land?

A

Around mid-Carboniferous (major radiation in Permian)

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5
Q

What are the defining features of Amniotes?

A
  • Waterproof integument (skin) ➡ reduced or no respiration
  • Developed lungs ➡ for respiration
  • Increasing complexity of the heart
  • Skeletal and skull changes ➡ locomotion and foraging
  • Muscle changes in head and body ➡ locomotion and foraging
  • Amniotic eggs ➡ **Most Important feature separating amphibians from all other Terrestrial vertebrates (Amniotes)
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6
Q

What is the Amniotic Egg?

A
  • cleido = Greek “closed”
  • Contains Amniotic fluid, Embryo, Yolk Sac, etc.
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7
Q

Amniotic Egg: Shell Features

A
  • Leathery or calcified shell **still subject to desiccation
  • Structural support in air
  • Allows gas exchange ➡ H2O, O2, CO2
  • Survival in drier areas
  • Size ➡ direct development
    - bypass larval stages; no gills
    - larger (fewer, higher surv.) offspring
  • Internal Fertilization
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8
Q

Amniotic Egg: Yolk Features

A
  • Nutrients; fuel
  • ALL vertebrates have extra embryonic membranes enclosing yolk
    ** i.e. not unique to amniotes
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9
Q

Amniotic Egg: Unique Components

A
  • Chorion: outer membrane for gas exchange
    Allantois, Amnion, Yolk sac all inside Chorion
  • Allantois: “bladder” that stores nitrogenous waste
  • Amnion: inner membrane providing cushion against mechanical shock
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10
Q

Amniotes split into what 2 major groups?

A
  • Synapsids and Sauropsids
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11
Q

What are the specialized characteristics that differ in Synapsids and Sauropsids?

A
  1. Locomotor systems compatible with higher rates of lung ventilation

2.Reduced lateral undulations ➡ leg positioning

  1. Respiratory and excretory systems to conserve H2O
  2. Ecto- ➡ Endothermy
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12
Q

Describe the lung ventilation and locomotion in Amniotes

A

Sprawling Gait: conflict between running and breathing, to combat this:

 - Locomotion & Respiration separated: for higher rates of lung ventilation

 - Reduced Lateral Undulations: changes in leg positioning

 - Respiratory and Circulatory systems changed
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13
Q

How do the brain structures differ in Synapsids vs Sauropsids?

A

Synapsids: good olfaction (smell), poor vision

Sauropsids: good vision, poor olfaction
- Specialize in diurnal activity

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14
Q

What is diurnal activity?

A

Active during the day, sleep at night

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15
Q

What is one of the main differences between Synapsids and Sauropsids?

A

The skull; separated by differences in the “temporal fenestration”

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16
Q

How do the anapsid, synapsid, and diapsid skulls differ between each other?

A

Anapsid: no fenestra between the postorbital and squamosal bone

Synapsid: one fenestra between the postorbital and squamosal bone

Diapsid: two fenestras between the postorbital and squamosal bone

17
Q

Why did the skull evolution provide for the Amniotes?

A

Increased complexity of jaw musculature and feeding; snapping vs chewing

18
Q

Which skulls belong to existing tetrapods?

A

Anapsid: Amphibians

Synapsid: Synapsids and Turtles A

Diapsid: Turtles B, Sphenodon, Lizards, Snakes, Crocodiles and Birds

19
Q

Anapsid Skull Information

A
  • Ancestral reptile condition
  • No fenestras; sometimes a notch at the back
  • Limits bite force
20
Q

Diapsid Skull Information

A
  • Two fenestras
  • Attachment of larger, stronger jaw muscles; jaw can open much wider
  • Allows animals to evolve away from “inertial snapping” (fish)
  • Allows evolution of different types of teeth for different needs
    • e.g. herbivore cropping/chewing vs carnivore tearing/shearing
21
Q

What orders make up the Sauropsids (Class Reptilia)?

A
  1. Testudines (Turtles)
  2. Lepidosauromorpha (Lizards and Snakes)
  3. Archosauromorpha (Crocodiles and Birds)
22
Q

When did the Sauropsids rise in evolution?

A

During the Permian-Triassic Extinction; ca. 250 mya

 - largest Extinction event ever

 - generated the Mesozoic ➡ Age of the Reptiles
23
Q

What are the Sauropsids defining features?

A
  1. Respiration
  2. Circulation
  3. Metabolism/-thermy
  4. Nitrogenous wastes
  5. Hearing
  6. Vision
  7. Olfaction
  8. Foraging
  9. Locomotion
  10. Reproduction
  11. Predator avoidance
  12. Adaptations to extreme conditions
24
Q

Is breathing on land easier than the ocean?

A

Yes,
- air has a higher oxygen content
- need less volume to meet metabolic demands
- air less dense and less viscous
- can pump easily over respiratory surfaces

25
Q

How did Sauropsids adapt to breathe on land?

A

The Aspiration Pump

26
Q

How does the Aspiration Pump work?

A
  • Negative pressure aspiration pump
  • Rib cage expanded using ribs or muscles to create negative pressure in the abdominal cavity; sucks air into the lungs
  • Complex subdivisions to increase surface area for gas exchange
27
Q

What allows air to flow through the nostrils into the mouth cavity in Sauropsids?

A

A palate

28
Q

How did the palate evolve to aid Sauropsids in respiration?

A

The partial palate in reptiles evolved to full secondary ones in Mammals and Birds
- Separates nostrils from the mouth; allowing them to eat and breath at the same time

29
Q

What did Sauropsids have to overcome on land for circulation purposes?

A

Gravity, blood pooling at extremities, blood has to be pumped using high pressure

However, gas exchange in lungs requires a low flow rate and pressure to allow diffusion of oxygen

30
Q

How does circulation work in Amniotes?

A

Amphibians:
- double-circuit
- 3 chambers
- incomplete separation of flow to lungs and skin

“Reptiles” (Turtles, Snakes, Lizards):
- double-circuit
- 3 chambers
- nearly complete separation of flow to lungs and body

31
Q

How did these adaptations in circulation aid Amniotes on land?

A

Breathing air; due to the two separate blood flow circuits

 - Systemic: transports oxygenated blood to the body (and back to the heart)

 - Pulmonary: transports deoxygenated blood to the lungs (and back to the heart)
32
Q

How did evolving to Ectothermy aid the Sauropsids on land?

A

Regulated their body temperature from external sources, e.g. the sun

The mechanisms of ectothermic thermoregulation can be behavioral or physiological

BIOL241 (5 decks)

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